Among methods of measuring the amount of moisture in soil, there exists an Amplitude Domain Reflectometry (ADR) method and a Time Domain Reflectometry (TDR) method, for example. These methods utilize the property that electric permittivity increase as the amount of moisture in soil increases. By electrically measuring the permittivity, the amount of moisture in soil is measured. Also, as a method of measuring the amount of moisture in soil, there exists a moisture content monitoring device that includes multiple electrodes able to be inserted into gardening soil. By measuring the electrical resistance value between these electrodes, the moisture content monitoring device measures the moisture content, and emits a warning sound in the case where the moisture content becomes less than or equal to a set boundary level (see Japanese Patent No. 2608679, for example).